//编写程序以 x 为基准分割链表，使得所有小于 x 的节点排在大于或等于 x 的节点之前。如果链表中包含 x，x 只需出现在小于 x 的元素之后(如下所示)。
//分割元素 x 只需处于“右半部分”即可，其不需要被置于左右两部分之间。 
//
// 示例: 
//
// 输入: head = 3->5->8->5->10->2->1, x = 5
//输出: 3->1->2->10->5->5->8
// 
// Related Topics 链表 双指针 
// 👍 58 👎 0


//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode partition(ListNode head, int x) {
        ListNode small = new ListNode(-1);
        ListNode sHead = small;
        ListNode large = new ListNode(-1);
        ListNode lHead = large;

        while (head != null) {
            if (head.val < x) {
                small.next = head;
                small = small.next;
            } else {
                large.next = head;
                large = large.next;
            }
            head = head.next;
        }

        large.next = null;
        small.next = lHead.next;

        return sHead.next;
    }
}
//leetcode submit region end(Prohibit modification and deletion)
